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United States Patent |
6,263,733
|
Reimer
,   et al.
|
July 24, 2001
|
Sensor for detection of acceleration and attitude within a vehicle
Abstract
A vehicle acceleration and attitude sensor is provided, having use as a
vehicle collision sensor for activation of air bags and the like, and as
well for detecting an unsafe angle or attitude of the vehicle. A
compressible carrier medium of light or other wave energy, such as
translucent foam, is coupled with a light or other wave energy source and
a receiver. An inertial mass, which may consist of the carrier medium
itself, is in contact with the carrier medium and operates to compress the
carrier medium when the apparatus is either accelerated or tilted beyond a
predetermined amount. A signal coupler and processor are associated with
the energy source and receiver. The apparatus operates on the principle
whereby compression of a scattering medium or an integrating cavity,
within the region surrounding a light or other wave energy source, will
increase the intensity of the wave energy. This increased intensity is
translated into a measurement of the acceleration or tilt experienced by
the sensor.
Inventors:
|
Reimer; Ernest M. (Oster Cove, CA);
Baldwin; Lorna H. (St. John's, CA)
|
Assignee:
|
Canpolar East Inc. (St. John's, CA)
|
Appl. No.:
|
449769 |
Filed:
|
November 26, 1999 |
Foreign Application Priority Data
Current U.S. Class: |
73/514.26 |
Intern'l Class: |
G01P 015/08 |
Field of Search: |
73/514.26
250/227.14,231.1
|
References Cited
U.S. Patent Documents
3587011 | Jun., 1971 | Kurz.
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3808697 | May., 1974 | Hall.
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4344235 | Aug., 1982 | Flanders.
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4430895 | Feb., 1984 | Colton.
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4627172 | Dec., 1986 | Afromowitz.
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4837537 | Jun., 1989 | Nakada et al.
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4912662 | Mar., 1990 | Butler et al.
| |
4967597 | Nov., 1990 | Yamada et al.
| |
5008774 | Apr., 1991 | Bullis et al.
| |
5350189 | Sep., 1994 | Tsuchitani et al.
| |
5351542 | Oct., 1994 | Ichimura et al.
| |
5356671 | Oct., 1994 | Drs.
| |
5373124 | Dec., 1994 | Abendroth et al.
| |
5388460 | Feb., 1995 | Sakurai et al.
| |
5412986 | May., 1995 | Beringhause et al.
| |
5436838 | Jul., 1995 | Miyamori.
| |
5452519 | Sep., 1995 | Crocker et al.
| |
5535626 | Jul., 1996 | Bullis et al.
| |
5571972 | Nov., 1996 | Okada.
| |
5594400 | Jan., 1997 | King.
| |
5623099 | Apr., 1997 | Schuster et al.
| |
5656846 | Aug., 1997 | Yamada.
| |
5676851 | Oct., 1997 | Suzuki et al.
| |
5719333 | Feb., 1998 | Hosoi et al.
| |
5748547 | May., 1998 | Mori et al.
| |
5917180 | Jun., 1999 | Reimer et al. | 250/227.
|
Primary Examiner: Moller; Richard A.
Attorney, Agent or Firm: McFadden, Fincham
Claims
We claim:
1. An acceleration sensor comprising:
a volume of compressible material, said material permitting the passage of
light generally freely therethrough while substantially fully scattering
light transmitted within said material;
a source of wave energy comprising light in operative communication with
said volume of compressible material for transmitting light into said
volume to form a region therein of substantially scattered wave energy;
support means for supporting said compressible material;
passive compression means for compressing said compressible material
against said support means in response to acceleration of said sensor for
causing an increase in in intensity of said wave energy within said
region;
a receiver for detecting the intensity of light within said region of
scattered wave energy;
signal processing means in operative communication with said receiver for
detecting the intensity of wave energy within said region of compressible
material and providing a selected output in response to acceleration
detected by said sensor.
2. A sensor as defined in claim 1, wherein said compression means comprises
said compressible material per se compressing in response to acceleration.
3. An acceleration sensor as defined in claim 1 wherein said wave energy
comprises light.
4. An acceleration sensor as defined in claim 3, wherein said source of
wave energy comprises a fiber optic line in communication with a light
source, and said receiver comprises a fiber optic line in communication
with a photo detector.
5. An acceleration sensor as defined in claim 1, where said compressible
material comprises light-translucent foam.
6. An acceleration sensor as defined in claim 1, further comprising a
housing, said compressible material, compression means, source of wave
energy and receiver being retained within said housing.
7. A sensor as defined in claim 1, wherein said compression means comprises
a member in contact with said compressible material.
8. An acceleration sensor as defined in claim 7 comprising an attitude
sensor, wherein said member is substantially fully surrounded by said
carrier medium, and wherein said source of wave energy and said receiver
comprises multiple wave energy sources and receivers disposed about 3 axes
surrounding said member for detection of increase wave energy intensity
indicative of movement of said member relative to said carrier medium, in
any direction.
9. An acceleration sensor as defined in claim 7 for acceleration detection
along one axis in two directions, wherein said compressible material
comprises first and second volumes, said member being positioned between
said first and second volumes, and further comprising first and second
sources and first and second receivers each coupled with a corresponding
of said volumes, wherein said member is mounted for compression of one of
said volumes when subjected to acceleration in a direction that falls on a
plane connecting said first and second volumes, to compress one of said
volumes for detection of acceleration of said sensor along one axis.
10. An acceleration sensor as defined in claim 9, wherein there is further
provided first and second retainer members on opposing sides of said
compressible material, said member comprising a plate substantially
spanning said upper and lower retainer members for sliding engagement
therewith.
11. An acceleration sensor as defined in claim 10, wherein bearing means
associated with said plate provide sliding engagement between said plate
and said retainer members.
12. An acceleration sensor as defined in claim 9, wherein fluid-filled
channels extend through said first and second volumes of said compressible
material and said member.
13. An acceleration sensor as defined in claim 12, for the detection of
acceleration events having an acceleration of between 10 and 50 g's, with
a duration of at least 10 milliseconds.
14. An acceleration sensor as defined in claim 7 for acceleration detection
along one axis in solely a single direction, wherein said compressible
material comprises a single volume bounded along one face by said member,
the opposed face of said compressible material being in operative
communication with said source and receiver.
15. An acceleration sensor as defined in claim 14, wherein said
compressible material is bounded along one face by a substrate, said
substrate being coupled to said source and receiver, and being further
coupled to said signal coupling means.
16. An acceleration sensor as defined in claim 14, wherein said substrate
comprises a printed circuit and said wave energy source comprises an LED
coupled to said substrate.
17. An acceleration sensor as defined in claim 7 wherein said compressible
material is generally cylindrical with a central annular opening, said
perimeter being generally disc shaped and substantially filling said
annular opening, and wherein at least three wave energy sources and
receivers are provided, said wave energy sources and receivers being
generally evenly distributed around the member of said compressible
material.
18. An acceleration sensor as defined in claim 17, wherein said member
comprises a fluid.
19. A sensor as defined in claim 17, wherein said member comprises a solid.
20. An acceleration sensor as defined in claim 7, wherein said compressible
material forms a hollow sphere, said member substantially filling the
hollow center of said sphere, there being further provided multiple wave
energy sources and receivers generally evenly disbursed around the
periphery of said carrier medium to detect acceleration or movement in any
direction.
21. An acceleration sensor as defined in claim 20, wherein said member
comprises a liquid.
22. An acceleration sensor as defined in claim 20, wherein said member
comprises a solid.
Description
FIELD OF INVENTION
The present invention relates to safety and control of vehicles, and in
particular sensors for determining the attitude and acceleration of a
vehicle. The present invention may be adapted as well for use in other
moving craft, including air, water, and space craft. Such sensors may be
used in association with air bags and other vehicle safety systems, to
control deployment of same. As well, such sensors may be used to measure
the tilt of a vehicle, for example to trigger a warning signal to
operators of off-road or construction vehicles.
BACKGROUND OF THE INVENTION
Vehicle safety systems, including air bags and seat belt tighteners are
conventionally triggered by various detection means and sensors, including
acceleration detectors, that detect rapid decelerations and accelerations
indicative of vehicle collision or impact. Further, attitude sensors to
detect the angle of inclination of a vehicle serve an important safety
function, including for example within all terrain, off-road or
construction vehicles.
The term "vehicle" herein refers to all manner of craft for use on land or
in air, water or space.
Conventionally, accelerometers comprise a frame, a mass, a spring-like
supporting system for suspending the mass within the frame for relative
movement within the frame, and damping means. Conventionally, an
electronic circuit translates mechanical movement of the mass into an
electrical signal. Most acceleration sensors operate mechanically with a
displacement or vibration of a moveable arm detecting acceleration. These
sensors measure displacement of an object from a specific reference point
to obtain an acceleration value. Common acceleration sensors used in
automotive safety restraint systems include capacitive, piezoresistive and
piezoelectric sensors. A further type of system is the "reed switch", as
disclosed within U.S. Pat. Nos. 3,587,011 and 5,594,400. In this
arrangement, a pair of magnets are arranged in inverted polar
orientations, producing opposed magnetic fields. A displacement of the
reed switch results in a change of magnetic field, triggering the safety
device.
Existing acceleration sensors suffer several drawbacks when implemented in
connection with a vehicle safety system. In particular, many existing
devices when conventionally manufactured have been found to have limited
sensitivity to a crash event and suffer from an inability to be "fine
tuned" to a particular acceleration level. While the sensitivity may be
increased to a suitable level, this typically entails unacceptably high
manufacturing costs. In the result, safety systems such as air bags are
prone to deployment either too easily or the opposite.
In addition to acceleration sensors, other sensors exist which determine a
vehicle's attitude. These sensors, which are well established within the
aerospace industry, may be used to determine a vehicle's inclination for
safety reasons. Conventional attitude sensors include a spherical ball
suspended in an inert fluid, out of contact with a housing which encloses
the assembly. The ball may include a magnet, whose orientation is affected
by the earth's magnetic field. Monitoring the orientation of this magnet,
which may be accomplished by the use of a pair of hall effect sensors
positioned opposite to one another within the housing, permits an
inclination reading. For example, see U.S. Pat. Nos. 5,452,519 and
5,356,671. A further prior art example is the linear servo accelerometer,
which consists of a pair of accelerometers mounted on a horizontal plane
at right angles to another. Any movement of the accelerometer from the
normal horizontal plane is detected as movement along the vertical axis.
See for example U.S. Pat. No. 3,808,697.
It is desirable to provide an improved acceleration and attitude sensor,
providing within a single, relatively inexpensive unit an accurate and
reliable detector of both acceleration and attitude. Such an apparatus may
have applications for the triggering of safety devices in vehicles, and as
well other useful applications within vehicles and other craft operating
on land, water, air and space. Superior acceleration and attitude
detection may be achieved through the use of a sensor which operates
according to principles of detection of compression of a medium within
which light or other wave energy is scattered, rather than strictly
electrical or mechanical means.
Within applicant's previous PCT International application no. PCTCA98/00686
there is disclosed a pressure sensor which operates according to the
principle whereby the intensity of light or other wave energy which is
dispersed and scattered within an integrating cavity, is increased as the
region within which the energy is dispersed is diminished. For example, as
the medium is compressed, the scattering region is diminished, resulting
in a detectable increase in the integrated or scattered light intensity.
According to this principle, a pressure sensor may comprise a compressible
carrier medium for light or other wave energy, containing scattering
centers for disbursing the light within the carrier medium. Wave energy
transmission and receiving means are associated with the carrier medium to
transmit and receive, respectively, the wave energy to and from the
carrier medium.
The term "light" will be generally used herein in reference to wave energy
of any suitable type. It will be understood that other forms of wave
energy including electromagnetic radiation in the non-visible spectra and
sound may comprise the wave energy for use in the present invention.
The carrier medium may be enclosed within a compressible housing such as a
flexible envelope or the like. Pressure applied to the housing compresses
the carrier medium, thereby increasing the intensity of the light within
the region surrounding the light source, in proportion to the decrease in
volume. The change in light intensity is detected by the receiver, which
transmits the information to a signal processing means. The carrier medium
preferably includes multiple light scattering centers evenly disbursed
throughout the medium. A suitable medium may be provided by a translucent
foam material. Alternatively, the interior face of the enclosure may
provide the light dispersion function. The enclosure comprises an
integrating optical cavity, which is defined as a region or volume either
bounded by an enclosure and comprising a deformable material with the
characteristic whereby illumination within the cavity undergoes multiple
scattering reflections or refractions to thereby become effectively
randomized and smoothed out in its distribution throughout the cavity. In
such a cavity, at the limit, information about the original direction of
illumination is eventually lost and the light becomes fully scattered. An
integrating optical cavity may be an air or gas filled enclosure, or may
be a volume within by a translucent solid such as an open-cell or closed
cell foam matrix that provides optical scattering sensors.
It is a characteristic of such a cavity that, for a light source with a
constant power output, the light intensity within the cavity is a function
of the volume of the cavity, the position of the light source and the
reflectance of the walls of the envelope. The cavity may be formed with
virtually any shape, although certain extreme shapes may not respond
ideally.
A pressure sensor of this type may take several convenient forms that are
adapted for the purposes of the present invention. For example, the sensor
may comprise an elongate, flattened member featuring multiple light
sources and receivers. Alternatively, the scattering medium may comprise a
block of foam shaped to fit within a defined cavity or receiving space.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a sensing or detection means
which may be mounted within a vehicle for detection of acceleration and/or
attitude of the vehicle. It is a further object to provide an improved
acceleration and/or attitude sensor, and to provide such a sensor as a
component of a vehicle.
The invention comprises in one aspect, a compressible carrier medium of
wave energy, preferably comprising a block of translucent material, the
carrier medium having wave energy scattering centers dispersed within it
to create a volume containing scattered wave energy upon the application
of wave energy to the medium;
a wave energy source coupled to and in substantial contact with the carrier
medium;
a wave energy receiver responding to the integrated intensity of scattered
wave energy within the carrier medium;
an inertial mass in contact with the carrier medium;
a support for supporting the carrier medium, inertial mass, energy source
and energy receiver; and
signal coupling means connected to the receiver for transferring signal
therefrom to a signal processing means, wherein the region around the wave
energy source and the receiver substantially defines these scattered
energy volume. The inertial mass contains sufficient mass, and is mounted
in an appropriate position, whereby a predetermined amount of acceleration
experienced by the device in a predetermined direction causes the inertial
mass to compress the carrier medium to increase the integrated intensity
of scattered wave energy sufficiently to trigger a response within the
signal processing means.
Preferably, the wave energy comprises light. The light source may comprise
an LED in contact with the carrier medium, or alternatively a fiber optic
cable, a transmitting end of which is in contact with the carrier medium
and the receiving end of which communicates with a remote light source. In
one aspect, the resiliency of the scattering medium, in combination with
the size, shape and mass of the inertial mass, permits discriminatory
detection of acceleration within the order of approximately 50 g's, and
having a duration in the order of approximately 1 millisecond.
In a further aspect, the inertial mass is retained between two separate
volumes of the carrier medium. Conveniently, a housing surrounds the
carrier medium, and the inertial mass is retained in position by means of
roller bearings or other slidable low friction contacts between the
housing and inertial mass. Within this arrangement, preferably each block
of carrier medium is associated with a respective energy source and
receiver. This arrangement is suitable for bidirectional acceleration
detection along a single axis.
In a further aspect, the energy source and receiver comprise a light
emitting diode and photo detector, respectively, the same both mounted to
a silicon chip substrate, which also supports a single unitary volume of
the carrier medium. An inertial mass is conveniently mounted to the
carrier medium at a position opposing the substrate. Within this aspect, a
supporting frame and suitable electrical contacts are conveniently
provided. In this configuration, single axis, unidirectional acceleration
may be detected. Alternatively, the separate inertial mass may be
dispensed with, and the function of this element is provided by the mass
of the carrier medium itself. This arrangement is suitable for detection
of relatively high impacts.
In a further aspect, a two axis multidirectional inertial sensor comprises
an inertial mass fully surrounded within one plane by a carrier medium,
with at least three and preferably four or more generally co-planar energy
emitters and detectors in contact with the carrier medium. Conveniently,
the inertial mass may comprise a central disk shaped or spherical member,
with the surrounding carrier medium comprising an annular disk or hollow
sphere which surrounds and contacts the central mass. This version may
also form a three axis multidirectional sensor by providing a mass fully
surrounded in all directions by the carrier medium. Wave energy
transmitters and receivers are mounted in multiple non co-planar positions
around the exterior of the carrier medium, or implanted within the carrier
medium and evenly spaced around the central mass.
In a further aspect, the foam density and inertial mass are selected to
achieve a mechanical resonance frequency higher or lower than the
frequency of the acceleration events to be resolved. In one version, the
density and mass are selected to provide a mechanical resonance frequency
above 1 kilohertz, for detection of automotive crash accelerations in the
order of 50 g's and a duration of approximately 1 millisecond. In a
further aspect, for the detection of impact events of between
approximately 10 and 50 g's, with a duration of approximately 10
milliseconds, the carrier medium resiliency and inertial mass are selected
to provide resonance frequency in the order of 1 hertz.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a single axis bidirectional accelerometer
according to the present invention;
FIG. 2 is a schematic view of a single axis unidirectional accelerometer;
FIG. 3 is a schematic view of a further embodiment as in FIG. 2;
FIG. 4 is a schematic view of a further embodiment of a single axis sensor;
FIG. 5 is a schematic view of a two axis multidirectional sensor; and
FIG. 6 is a schematic view of a three axis multidirectional sensor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning to FIG. 1, a first version of the device 10 detects acceleration
along a single axis, within two directions (as indicated by the arrow),
and is specifically adapted for detection of relatively high acceleration,
brief duration events. Within this version, the device 10 comprises a
housing 12 featuring upper and lower parallel generally planar retainers
14. An inertial mass is positioned vertically within the housing, and
conveniently comprises a metal plate 16. The plate is mounted for
longitudinal movement in the direction of acceleration detection, namely
axially along the longitudinal axis of the housing, in the forward or
rearward direction. Bearings 18 or the like slidably engage the plate 16
within the interior of the housing 12, to facilitate gliding of the plate
within the housing. The plate 16 is retained in a vertical position,
substantially transversely spanning the housing. The plate thus separates
the housing into forward and rear compartments 20 and 22, aligned in the
direction of impact detection. A block of translucent foam 24 or other
suitable carrier medium is disposed within each compartment, in contact
with the transverse plate the lower retainer 14 comprises a support for
the foam block 24.
Two light emitter detector units 26(a) and (b) are mounted within the
housing, at respective ends of the housing and in contact with the foam
blocks 24. The foam blocks are each thus sandwiched between a
corresponding emitter/detector unit and the transverse plate. The
emitter/detector units may comprise a pair of fiber optic fibers bundled
together to form a cable, whereby a first of the fibers comprises an
emitter and the second comprises a detector. Alternatively, the unit may
comprise an LED and a photo receptor in direct contact with the carrier
medium.
The emitter/detector units are each connected by cable 28 to a control and
processor unit 30. In the case of a fiber optic light emitter the
processor further includes a light source such as an LED in communication
with the corresponding light emitter fiber and a photo receptor in
communication with the receptor fiber. The structure and functions of the
control unit are essentially the same within all embodiments of the
invention, and will be described in detail below.
The control unit 30 is connected to a power source, not shown, and is
further connected to a safety system which responds to a vehicle impact,
such as an air bag, seat belt tightener or the like (not shown).
A further version is illustrated within FIG. 2, and comprises a relatively
compact single axis unidirectional accelerometer 40. The device includes a
rigid housing 42, mounted to a flat base 44. A planar silicon chip
substrate 46 is mounted within the compartment, conveniently on or
adjacent the base. The substrate supports a light emitting diode 48 on the
upper surface thereof, and a photo detector 50 adjacent thereto.
Electrical leads 52 extending through the base provide power to the
substrate, and transmit electrical signals therefrom. The substrate
comprises a conventional LED and photo detector circuit.
A block of translucent foam 54 or other like carrier medium overlies the
substrate and the LED and photo detector. An inertial mass, comprising a
metal plate 56 or the like, caps the block of carrier medium. Within this
version, force in the direction indicated by the arrow, i.e. acceleration
of the detector in the direction opposite the arrow, compresses the
carrier medium between the inertial mass and substrate, thereby increasing
the intensity of the illumination in the region surrounding the light
source and reducing the intensity of illumination at some remove from the
source the flat base 44 comprises a support for the substrate 46, foam
block 54, doide 48, and detector 50.
FIG. 3 illustrates a variation of the embodiment shown in FIG. 2. In this
version, the light source and detector comprise unitary fiber optic
emitters and detectors 58. This version thus comprises a base 60 and
housing 62, with the carrier medium 64 and emitter/detector 58 unit being
supported by or fastened to the base. Within this version, the inertial
mass comprises simply the mass of the carrier medium, which in the event
of a sufficient amount of acceleration will compress, resulting in
increased light intensity in the region surrounding the light
emitter/detector. This arrangement is suitable for detection of very high
g forces.
FIG. 4 illustrates a single axis, bidirectional detector 70, similar to the
version shown in FIG. 1, but specifically adapted for the detection of
relatively low acceleration, long duration events. In this version, an
elongate housing 72 contains a centrally disposed inertial mass 74 which
divides the housing into front and rear compartments 76(a) and (b) aligned
along the direction of acceleration detection. The front and rear
compartments each house a block of relatively soft carrier medium 78. The
inertial mass in turn is relatively large and has a relatively high mass
in comparison with the high acceleration, low duration detector
exemplified in FIG. 1. Two emitter/detector units 80 are positioned on
respective ends of the housing, opposing the central inertial mass, and
are connected to a control unit as described above.
The assembly is fitted with a low friction bearing surface 82 within the
interior of the housing, which allows relatively free travel of the
inertial mass. In order to increase the device sensitivity, fluid-filled
channels 84 extend longitudinally through the carrier medium and inertial
mass. The foam carrier medium 74 has an elastic constant that is just
large enough to hold the inertial mass in place in a zero g or sub g
threshold acceleration situation. This design makes use of elastic foam or
lattice structures as the carrier medium which show a high stiffness at a
zero deformation but once deformed, have a much lower stiffness. In this
assembly the inertial mass encounters low resistance to displacement once
the acceleration exceeds a specified intensity threshold. The resonant
frequency of the assembly is relatively low. Of particular interest to
vehicle applications is detection of events having an acceleration of 10
to 50 g's, with a duration in the order of 10 milliseconds. Resonance in
the order of 1 hertz within the device will ensure that these events are
resolved. In order to achieve this level of sensitivity, the sensor must
be relatively long in the direction of acceleration detection. Since a 50
g, 30 millisecond event, will displace the seismic mass by about 20
millimeters, the overall length of the device may be in the order of 100
millimeters.
It will be seen that any of the above single axis sensor will in fact
detect acceleration along any axis which is offset from the main axis,
with the efficiency of detection declining to zero as the angle increases.
Thus, any of these arrangements can be used whereby detection is required
within a relatively narrow range centered on a single axis.
A two axis multidirectional sensor is illustrated within FIG. 5. In this
version a cylindrical housing 90 contains a centrally disposed disk-shaped
inertial mass, comprising a metal disk 92. An annular space is defined
between the central inertial mass and the interior of the housing 90, with
this space being substantially filled by a foam carrier medium 94. At
least three and preferably four emitter/detector units 96 are positioned
around the perimeter of the carrier medium and in communication therewith.
The emitter/detector units are linked to a processing unit 30 as described
below. Within this version, acceleration along the two axes shown by
arrows within FIG. 5 as well as any intermediate direction, may be
detected.
A further variant of the embodiment shown in FIG. 5 comprises a three axis,
multidirectional sensor 100. In this version, illustrated in FIG. 6, the
housing 102, carrier medium 104 and central inertial mass 106 comprise
concentric spherical members. Multiple emitter/detector units 108 are
evenly positioned about the periphery of the carrier medium, in much the
same manner as described above. The central mass may comprise a solid
metal sphere, or a liquid body retained within a leakproof central cavity
within the carrier medium 104.
The three axis sensor is capable of resolving roll, pitch and yaw in any
direction, as indicated by the arrows in FIG. 6. The inertial mass 106 may
comprise a liquid having a viscosity selected to damp modal vibration of
the assembly. The resonance frequency of the assembly will typically be
higher then the time scale of events of interest.
The embodiments illustrated in FIGS. 5 and 6 are intended specifically to
comprise rate or attitude sensor configurations. Rate sensors detect rate
of turn by detecting rotational accelerations or centrifugal
accelerations. Attitude or inclination sensors operate by detecting
off-axis gravitational accelerations. For automotive applications, these
sensors are tuned for optimal operation at accelerations in the order of
+/-1 g.
Although the present invention has been described by way of a preferred
embodiment thereof, it will be seen by those skilled in the art to which
this invention relates, that departures from these described embodiments
may be made while still remaining within the scope of the invention as
defined by the claims of this patent specification.
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